These data describe whole-brain properties and circuits, as well as contain new methods to classify cell types based on connectivity. A number of new tests for estimating the completeness and accuracy were required and therefore developed, in order to verify the correctness of the connectome. Producing this data set required advances in sample preparation, imaging, image alignment, machine segmentation of cells, synapse detection, data storage, proofreading software, and protocols to arbitrate each decision. For simplicity, we will often state that the hemibrain contains ≈25K neurons. Note: (1) our definition of cropped is somewhat subjective (2) the usefulness of a cropped neuron depends on the application and (3) some small fragments are known to be distinct neurons. A neuron is considered uncropped if most arbors (though perhaps not the soma) are contained in the volume. For the table, a neuron is traced if all its main branches within the volume are reconstructed. The highlighted area shows the portion of the central brain that was imaged and reconstructed, superimposed on a grayscale representation of the entire Drosophila brain. Performing a similar analysis on the brain of a small mammal, by scaling up the methods here, will be a likely next step along this path. In the long run, studying the fly connectome may therefore lead to a better understanding of the human brain and its disorders. Many of these findings will likely apply to larger brains, including our own. When used in combination with existing methods, the map will make it easier to understand how the fly brain works, and how and why it can fail to work correctly. The central brain connectome is freely available online for anyone to access. used the new connectome to obtain further insights into the circuits that support specific fruit fly behaviors. A three-dimensional map of the neurons and connections in the brain was then reconstructed from these images using machine learning algorithms. To prepare the map – or connectome – the brain was cut into very thin 8nm slices and photographed with an electron microscope. The central brain consists of approximately 25,000 neurons and around 20 million connections. prepared the first complete map of the entire central region of the fruit fly brain. To solve this problem, Scheffer, Xu, Januszewski, Lu, Takemura, Hayworth, Huang, Shinomiya et al. This is like trying to understand a novel when all you can see is a few isolated paragraphs. This is because previous studies showing the connections between cells only covered small areas of the brain. But exactly how they do this is often unclear. Thanks to decades of research, scientists now have a good understanding of which parts of the fruit fly brain support particular behaviors. But it nevertheless supports a range of complex behaviors, including navigation, courtship and learning. With about 100,000 neurons – compared to some 86 billion in humans – the fly brain is small enough to study at the level of individual cells. The fruit fly Drosophila is a popular choice for such research. Studying the brain of any one animal in depth can thus reveal the general principles behind the workings of all brains. eLife digestĪnimal brains of all sizes, from the smallest to the largest, work in broadly similar ways. Biologically, we examine distributions of connection strengths, neural motifs on different scales, electrical consequences of compartmentalization, and evidence that maximizing packing density is an important criterion in the evolution of the fly’s brain. We make the data public and simplify access, reducing the effort needed to answer circuit questions, and provide procedures linking the neurons defined by our analysis with genetic reagents. We provide detailed circuits consisting of neurons and their chemical synapses for most of the central brain. We define cell types, refine computational compartments, and provide an exhaustive atlas of cell examples and types, many of them novel. Improved methods include new procedures to prepare, image, align, segment, find synapses in, and proofread such large data sets. We summarize new methods and present the circuitry of a large fraction of the brain of the fruit fly Drosophila melanogaster. The neural circuits responsible for animal behavior remain largely unknown.
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